Cyanide leaching is one of the main technologies of gold extraction. For this technology, the cyanide leaching recovery rate is determined by the efficiency of the leaching operation. Under the condition of maintaining the cost of the processing plant and increasing the technology economical efficiency, how to apply the reasonable leaching technology and equipment, and how to choose the reasonable leaching conditions. These need to be determined by the gold cyanide leaching experiment. The experiment items are the same as the factors influencing the gold leaching process.
Use the table of contents below to navigate through the guide:
The gold monomer dissociation or a bare gold surface is the essential condition of cyanide leaching, while the grinding fineness is the important factor influencing the monomer dissociation. To make sure the high index of cyanidation, it needs to research the influence of the particle size for cyanide leaching to determine the suitable grinding fineness according to the material characteristics.
The mineral monomer dissociation in the ore is the key problem to be solved before the processing of all kinds of processing technologies. Only the monomer dissociation of most minerals can guarantee a high recovery rate and reduce the lost in tailings as possible.
However, it should be noted that the over-grinding should be avoided in purchasing a small particle size of ore. It not only increases the grinding costs, but also increases possibility of the leachable impurities into the leaching solution. It can also cause the difficulty of solid-liquid separation, and the lost of cyanide and dissolved gold. Therefore, the grinding fineness needs to be measured by cyanide leaching experiment in a further way.
The leaching time is one of the important factors influencing the gold leaching process. During the leaching processs, the leaching rate of gold increases gradually with the time, but the leaching rate decreases continuously due to the thickness of the saturated solution layer on the gold surface increases gradually, and the leaching rate gradually tends to a constant value.
It is necessary to make sure the suitable leaching time in the cyanide leaching process. The leaching time is short, the gold mineral can’t fully dissolve and leach; the leaching time is too long, it needs larger equipment and site deployed, and leads to the impurities dissolution and impeding the dissolution of gold.
CN- is not stable in the solution, which is easy to volatile as HCN. The lime is added as the protective alkali to maintain the pH value. The addition of lime is to avoid the volatilzation of cyanide, and also reducing the consumption of cyanide by reacting with iron ions into iron hydroxide precipitation.
In the actual production, the amount of lime should be controlled strictly. The pH value is usually 10-11. If the lime amount is too much, pulp viscosity is increased because of the flocculation. It also increases the solvent diffusion resistance, so is the impurities in the solution and the pollution of the gold surface. It can also form a calcium oxide film on the gold particle, which blocks the reaction of sodium cyanide and oxide, reducing the leaching effort. If the lime amount is little, on the one hand, it will increase the consumption of sodium cyanide and affect the leaching index. On the other hand, increase the turbidity of your liquid, causing the washing thickener to run the tank. To make sure the suitable lime amount, It is necessary to carry out a condition test of lime dosage.
The slurry concentration directly influences the gold leaching speed and leaching rate. The bigger concentration is, the worse the pulp viscosity is, the worse liquidity is, so is the gold leaching speed and the leaching rate; Otherwise, the lower concentration is, the better the pulp viscosity is, the higher gold leaching rate is. However, it also increases the agent amount in times, and so is the equipment volume and the investment cost. Therefore, to balance the gold leaching rate and the production cost, the suitable slurry concentration is necessary.
In the gold cyanide leaching process, in a certain scope, the amount of cyanide is positively related to the gold leaching rate. However, if the cyanide amount is too high, increasing the costs, but the leaching rate of gold did not change much. At the same time, the adding mode of cyanide also influences the gold leaching rate and leaching speed to a certain extent.
Therefore, on the basis of grinding fineness test, in order to further reduce the dosage of cyanidation agent and the production cost, and to determine the addition method of cyanidation agent, the dosage and addition method of cyanidation agent should be tested.
The associated mineral dissolves in cyanide solution to different degrees, which has an adverse effect on gold leaching. This kind of gold cyanide leaching need to be pretreated. Oxidation pretreatment with oxidants can effectively improve the recovery rate of cyanide leaching. A pretreatment agent selection test is needed for gold ore leaching. The pretreatment agents are calcium peroxide, sodium hypochlorite, sodium peroxide, hydrogen peroxide, citric acid, lead nitrate, etc. In general, the leaching effect after pretreatment is compared with that without pretreatment under normal conditions. The purpose is to determine whether a pretreatment job is required.
The above is the items of gold cyanide leaching experiment. It is suggested that before the design of the concentrator, a factory with the qualification of the concentrator should be commissioned to carry out the concentrator test.